How is steel annealed?

• A. Heated to just above its upper critical temperature until it reaches a uniform temperature throughout, then cooled very slowly in the oven.
• B. Quenched in water.
• C. Cooled rapidly in air.
• D. Coated with protective layer.

Answer: (A)

Annealing softens and relieves stresses in steel by transforming its microstructure through a controlled heat cycle. The process involves heating the steel to a temperature above the upper critical point so the structure becomes austenite throughout, then cooling it very slowly in the furnace. This slow, uniform cooling allows atoms to diffuse and the grains to reorganize, reducing hardness and increasing ductility and machinability. Quenching in water or rapid cooling in air hardens steel, which is the opposite effect of annealing, while coating with a protective layer has no effect on the heat-treated microstructure.